I. Field of the Invention
This invention relates to a gate valve and, in particular, to a lubricated seat within the gate valve which enhances the sealing properties of the seat while facilitating pressure testing of the seal.
II. Description of the Prior Art
Gate valves have been commonly used for many years and have been employed in a variety of services such as in the oil and gas services of the petroleum industry. Such valves are designed for service involving pressures of several thousand pounds per square inch and must be capable of closing off flow through the conduit associated with the valve. Typical gate valves generally consist of a valve body having inlet and outlet conduits with a valve chamber therebetween. A gate having an opening therethrough is disposed in a valve seat mounted within the chamber and the gate is mounted on a stem. The stem reciprocates within the chamber for moving the gate between a closed position in which flow is blocked and an open position in which flow is through the gate opening. A gate seat seals flow past the gate by engaging the gate. Typical of such valve seats are block and bleed seals which feature upstream and downstream primary and secondary seals to provide greater sealing capacity under extreme fluid pressures.
The prior known block and bleed seals are mounted within the gate valve and dependent upon the lubricating properties provided by the fluid environment. Such dependence can result in unanticipated wear and eventual failure of the seat. In the past users have regularly tested the valve seats by blowing the entire valve contents out to atmosphere to ensure seat integrity. A lubrication system associated with the valve seat would provide a continuous supply of lubricant to the valve seat.